1. Technical Field
This invention relates to machines which transform extruded thermoplastic into a corrugated plastic tile and more particularly to machines which can be continuously form corrugated plastic tiles.
2. Description of the Prior Art
Due to the utility of corrugated plastic tiles particularly as buried drainage conduits, a need has arisen for devices which can continuously mold lengths of corrugated plastic tiles.
One such type of device is found in U.S. Pat. No. 3,981,663 issued Sept. 21, 1976 to Lupke. Acting in conjunction with a thermoplastic extruder which continuously dispenses a cylindrical tube of heated, pliable plastic, the corrugator has upper and lower mold assemblies each of which consists of endless chains of mold blocks. Synchronously driving the upper and lower mold assemblies causes the individual mold blocks thereof, with the aid of aligning pins, to mate and run together for a portion of the corrugator to form a tunnel defining a tubular mold which receives, moves with and molds the dispensed thermoplastic. At the end of the molding run the mold blocks are drawn substantially radially away from the molded corrugated tile so as not to damage the corrugations formed thereby.
One of the drawbacks of corrugators heretofore used and particularly of the type described above is that they tend to be quite large and therefore require large areas of dedicated space. One of the primary factors contributing to the size of the machine is the requirement that the mold blocks be drawn substantially radially away from the tile at the end of the molding operation so that the corrugated surfaces of the mold blocks do not engage and thereby damage or distort the corrugations.
Another drawback of note is the method by which the mold blocks of the upper and lower mold assemblies are matingly brought together to form the tunnel in which the corrugated tile is molded. Synchronous drives for both the upper and lower mold assemblies are required along with aligning pins on individual mold blocks to assure that the mold blocks properly mate to form the molding tunnel. Occasional slack, induced upon the chains carrying the mold blocks by wear, may result in the failure of the mold blocks to properly come together thereby creating random seams or the like along the corrugated tile or, if the amount of slack is great enough, shearing off the aligning pins on the mold blocks necessitating stopping of the corrugator for replacement thereof.
Yet a further drawback of corrugators heretofore used is that the driving motors, due to the friction between the mold blocks, their interconnecting chains and the frame, must be of substantial horsepower to drive the mold assemblies.
It is an object of the present invention to overcome the drawbacks of corrugators heretofore used particularly those drawbacks set forth above.